Web casting apparatus



Oct. 20, 1970 D. w. BUSHNELL ETAL 3,534,438

WEB CASTING APPARATUS Filed July 1, 1968 A TTORNEYS WEB CASTING APPARATUS 3 Sheets-Sheet 2 Filed July 1, 1968 U M M U B W 0 m M 0 0 M P m m D M W S m T N V m A TTOH/VEYS Oct. 20, 1970 D. w. BUSHNELL ET AL WEB CASTING APPARATUS 5 Sheet$-$heet 5 Filed, July 1. 1968 DONALD w BUSHNELL WALDEMAR PABO INVENTORS & M

Uh llm Ml Him $35 QREQU EQRDQQM GER M U mwmaqmuxm k 5: Q3 E 2E E:

3,534,438 WEB CASTING APPARATUS Donald W. Bushnell, Webster, and Waldemar Pabo, Hilton, N.Y., assignors to Eastman Kodak Company,

Rochester, N.Y., a corporation of New Jersey Filed July 1, 1968, Ser. No. 741,753 Int. Cl. B29d 7/10 US. Cl. 18-15 7 Claims ABSTRACT OF THE DISCLOSURE A casting wheel having inner and outer shells and end plates to define a chamber. The chamber is partially filled with a heat-conductive fluid. A heating coil mounted adjacent the inner surface of the inner shell supplies heat to the fluid. When the wheel is rotated, the fluid immediately adjacent the inner shell mixes with the rest of the fluid in the chamber resulting in a more effective transfer of heat from the coil to the casting surface.

BACKGROUND OF THE INVENTION This invention relates to a casting wheel for casting, transporting, and drying a web. More particularly, the invention relates to such a casting Wheel which has a captive body of fluid confined therein to more effectively transfer heat from the heat source to the casting wheel surface.

In the production of flexible film or webs, it is customary to extrude or cast a liquid solution onto a rotating cylinder, drum or wheel having a smooth casting surface. As the wheel rotates from the point where the liquid solution is placed on the casting surface, the solvents contained in the solution are evaporated off and a film is formed. When enough solvent has been evaporated off, the film becomes self supporting and is stripped from the casting wheel.

In order to expedite the evaporation of solvents from the liquid to more rapidly form the film, it is customary to apply heat to the casting wheel. One of the most critical problems on casting a web or film is to distribute the heat evenly across the casting surface. If the heat is properly distributed across the casting surface, the fluid deposited thereon will dry at an even rate resulting in a high quality product that has a uniform cross section and is free of surface defects. However, if the heat is not applied evenly, the solvent is driven off at different rates across the drum surface thereby causing uneven shrinkage in the film during the casting process and resulting in a poor, low quality product that has an uneven cross section and surface defects.

Various methods and apparatus have been devised attempting more accurately to control the temperature across the casting surface. For example, many casting wheels have been devised with complex piping systems and fluid passages built therein to provide heating fluid to the casting wheel and distribute the heat evenly across the wheel surface by controlling the circulation of heating fluid. Other wheels were devised with baffles and scoops to assist in keeping the heating fluid in contact with the casting wheel. In some cases to maintain even temperature in the wheel, it is often required to pump large quantities of fluid into and out of the wheel. However, in casting wheels through which water is pumped, there is the problem of hot spots. Where passages and conduits are United States Patent O 3,534,438 Patented Oct. 20, 1970 ice provided to convey the fluid to the casting shell, the path of the water is constant, resulting in a heat pattern, which conforms to the passage pattern inside the wheel, on the casting surface.

Furthermore, with the complicated piping required, the hazards of causing hot spots in the casting surface from metal to metal contact inside the drum is greatly increased. Along with the piping systems also goes the added problems of casting wheel weight and maintaining good pressure seals.

In addition to the problems incurred in properly distributing the heat across the main portion of the casting surface, there is also the critical problem of properly maintaining edge temperature of the casting wheel. If the edge temperature of a casting wheel is not properly controlled, the excess heat causes hot spots near the web edges again resulting in an inferior product.

The need has long existed for a casting wheel which embodies the desirable heat distribution characteristics of a system utilizing a heat-conductive fluid immediately adjacent the casting surface yet offers a simple efficient system to supply heat to the drum.

The further need has existed for a cooling system which could more effectively remove excessive undesired heat from the casting wheel edges.

SUMMARY OF THE INVENTION The present invention is a simple straight-forward apparatus for transmitting heat from the inside of a casting wheel to the casting surface of the wheels while accurately maintaining the temperature across the Wheel surface.

The present invention further comprises an apparatus for transferring heat from the inner shell of a casting wheel to the outer shell with a low temperature differential across the heating chamber.

The present method is adapted for use in a casting wheel which comprises an inner or outer cylindrical shell. End plates are provided at the ends of the shells to define a chamber therebetween which is partially filled with a heatconductive fluid. A heat source is mounted adjacent to the inner shell around the inner periphery of the shell. The entire casting wheel is provided with an axle so that it is rotatably mounted in a manner conventional in such casting apparatus.

Heat is applied through a heat source to the inner shell and is transferred to the heat-conductive fluid. The rotating motion of the casting lwheel relative to the body of fluid contained in the chamber causes currents in the fluid which aid in the mixing of the layer of fluid nearest the inner shell 'with the remainder of fluid in the chamber. The currents assist in the transfer of heat through the conductive fluid to the outside Wall. The heat is then transferred by natural conduction through the outer shell to the casting surface.

In a preferred embodiment of the invention, the heat source is a serpentine coil mounted such that the coil eX- tends transversely across the inner shell around the inner periphery of the shell. The heating coil is provided with hot fluid "from a source outside of the casting wheel. The heat-conductive fluid in the preferred embodiment is water; however, it can be any good heat-conductive fluid.

The present invention also provide for a novel method to cool the edges of a casting drum. The casting drum of the present invention is provided with chambers that extend around the wheel underneath the casting surface near the wheel edges.

Both chambers are partially filled with a heat-conductive fluid. A cooling coil located in each cavity is provided with cooling fluid from an outside source.

Heat flows from the casting wheel surface through the heat-conductive fluid in the cavity to the cooling coil which removes the heat from the wheel.

The rotating movement of the wheel causes currents in the cooling fluid which assist in the transfer of heat from the casting wheel to the cooling coil.

The various features of novelty which characterize the invention are pointed out with particularly in the claims annexed to and forming a part of the specification. For a better understanding of the invention, the operating advantages and the objectives obtained by its use, reference should be had to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention has been illustrated.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional view partly broken away showing the internal structure of the casting Wheel 7 along view 1-1 of FIG. 2.

FIG. 2 is a side view partly broken away showing the structure of the wheel.

FIG. 3 is a schematic showing essential components of the present casting wheel.

FIG. 4 is a side view partially broken away showing the casting wheel mounted in an air chamber.

DESCRIPTION OF THE PREFERRED EMBODIMENT The casting wheel of the present invention has an outer shell 2 and inner shell 4 which is connected with and joined to the outer shell by means of end plates 6 thereby forming a chamber 8 between the shells. The width of the outer shell is greater than that of the inner shell such that the outer shell overhangs the chamber at the sides of the casting wheel.

Flanges 10 are attached to the ends of the outer shell 2 and extend inwardly around the edges of the shell. A plurality of channel irons 12 extend longitudinally across the casting wheel between the flanges 10 and are attached at both ends to the flanges 10. The channel irons 12 and flanges 10 provide the means by which the spokes 14 support the casting surface 1 and connect it to the shaft 16. The spoke 14 is connected at one end to the shaft 16 and extends radially outward to be connected at the opposite end to the channels 12. In one embodiment of the present invention the spokes are formed such that from a side view such as in FIG. 2, they are Y-shaped, with the single leg of the Y connected to the shaft 16 and each of the two upper arms of the Y connected to a channel 12. The shaft 16 extends longitudinally beyond the side of the shell so that the entire wheel can be rotatably mounted in journals or pedestals. A more detailed description of the channel irons and spokes that support the shells around the shaft is disclosed in US. application Ser. No. 741,669, filed simultaneously herewith, now abandoned.

A serpentine heating coil 18 is mounted on the inner surface 20 of the inner shell 4 around the inner periphery of the shell and extends across substantially the full Width of the shell. A heated fluid such as hot water is passed through the coil. The fluid is heated at a heat exchanger 32 remote from the casting wheel and enters the casting wheel through a pipe 34 which extends through the passage 36 in the shaft to the heating coil 18. When the heated fluid has travelled through the length of the serpentine coil 18, it is returned through a return pipe 38 which connects the coil 18 to the bore 36 in the shaft whereupon it is transferred back to the heat exchanger 32 through a pipe 33.

The heating coil can be divided into several circuits having their own respective supply and return lines. For example, FIG. 1 shows the supply pipe 34 connected to the coils 18, and the return pipe 38 connected to the shaft bore 36. FIG. 2 shows additional supply and return pipes numbered 34' and 38, respectively. When the heating coil is divided into two or more circuits the heat supply to the heating chamber can be regulated with more sen sitivity than when the heating coil is a single unit.

A serpentine coil 18 was selected as the heating supply means because of the ability of such a coil oriented transversely across the inner periphery to average the temperature across the fluid chamber 8. The coil 18 tends to distribute the heat more evenly to the fluid chamber 8.

A chamber 8 is partially filled with a heat-conductive fluid, such as water; however, any suitable heat-conductive fluid can be used. The fluid is placed in the chamber through a fill hole which is plugged and sealed when the chamber has been filled to the desired level. It has been found that the optimum heat transfer is effected when the chamber is to 99% filled, however slightly more or less fluid may be used.

In operation the wheel is mounted in a web casting machine and turned by suitable driving means, such as a drive motor 42. Immediately adjacent to, at or near the top of the wheel, is mounted the container 44 which is filled with the casting solution. The solution is allowed to pour from the container onto the casting surface 1. As the wheel rotates, heating fluid is pumped from the heat exchanger 32 through the serpentine coils 18 and back to the heat exchanger 32.

The heat from the coils 18 is transmitted and distributed to the inner surface 20 of the shell 4 and is in turn transmitted by conduction to the water in the chamber 8. The motion of the chamber 8 or shells relative to the body of fluid causes the layer of water immediately adjacent to the inner shell 4 to mix with the water in the chamber 8. This mixing causes the heat to be transmitted to the outer shell 2 whereupon the heat is conducted through said outer shell 2 to the casting surface 1.

When the chamber is completely filled, the motion of the wheel has little effect on the transmission of heat from the heating coils across the chamber to the casting surface and the temperature differential between the heating coils and the casting surface is high. Because of the high temperature differential across a completely filled chamber, higher temperatures must be used in the heating coils to achieve a given temperature at the casting surface. With the higher temperatures in the coils, the chances for hot spots developing on the casting surface are greatly increased. The heat is conducted through the chamber walls and develops hot spots where the end plates connect to the outer shell. Furthermore, in a filled chamber there is no relative motion between the fluid body and the shells, therefore the heat flow is practically linear through the chamber from the inner shell 4 to the outer shell 2. Hot spots developed on the inner shell 4 are conducted through the chamber as a hot spot on the outer shell 2.

The temperature drop across a partially filled chamber is much less than the temperature drop of differential across a completely filled chamber. Therefore, in order to maintain a given temperature at the casting surface of a wheel, much less temperature is needed in the coils.

For example, in order to deliver 200 B.t.u./ft. across a completely filled fluid chamber in a rotating wheel of approximately 4 to 20 feet in diameter moving at a surface speed of 30 to 400 feet per minute, the temperature drop from one wall to the other wall across approximately two inches of water will be approximately 100 F. However, in a wheel of similar dimensions wherein the chamber is partially filled with water, the temperature drop across the chamber is approximately 4 that of a filled chamber. Therefore, if it is desired to maintain a temperature of approximately 100 F. at the surface of a casting wheel having a partially filled chamber, the temperature in the heating coils must be approximately F. Of course, account must be made for the slight drop across the chamber walls. In a wheel having a completely filled chamber, the temperature in the heating coils must be approximately 200 F.

An additional benefit of the present heating system can be shown by comparing it to a casting wheel wherein the heating fluid is continually pumped through the heating chamber from an outside source. It is estimated that in such a wheel wherein it is desired to deliver 200 B.t.u./ft. of heat to the casting surface that 290 gallons per minute of heating fluid would have to be pumped through the chamber. Furthermore, in such wheels it is customary to devise complicated passageways inside the wheel to distribute the heated fluid evenly beneath the shell. Complicated pumps and piping systems are also usually required to convey the fluid to and from the Wheel.

Cooling chambers 22 are located adjacent the edges of the casting wheel and extend circumferentially around the inner periphery of the outer shell 2. A cooling coil 24 is provided in each chamber 22 and extends circumferentially around the wheel inside the cooling chamber 22. The cooling coil 24 is provided with a cooling fluid from a cooling fluid heat exchanger 46 Outside the wheel. The cooling fluid is conducted from the cooling fluid heat exchanger 46 to the coil through a pipe 28 to the cooling coil 24. The return also flows through pipes 30, through a passage 31 in the shaft, and back to the cooling fluid heat exchanger 46 through a pipe 45.

The cooling chamber 22 is partially filled with a heatconductive fluid. The chamber is first partially filled with fluid by conventional means and sealed off to form a captive body of fluid similar to the heating chamber. In operation, the wheel is rotated and cooling fluid is pumped through the cooling coil 24. The heat from the casting surface 1 is conducted through the shell to the conductive fluid in the cooling chamber 22. The heat is then conducted through the heat-conductive fluid to the cooling coils 24 and is subsequently removed from the wheel. The flow of cooling fluid to the wheel and the fluid temperature can be controlled by an operator depending upon the degree of cooling necessary to stabilize and control the temperature of the casting surface.

In many web casting machines in addition to the heat provided to the interior of the wheel to dry a film, heat in the form of hot air is also provided around the wheel to assist in drying the film. Normally it is heat from the hot air that causes a rise in edge temperatures on the casting wheel and the need for cooling the wheel edges. FIG. 4 shows the wheel of the present invention mounted in an air chamber 50. Hot air is supplied to the chamber 50 through suitable conduits 52 and flows past a portion of the casting surface to assist in removing the solvent from the web 54. The air is then removed from the chamber 50 through an exhaust conduit 56. FIG. 4 also shows a casting solution container or coating hopper 44 from which the casting solution is dispensed.

As the wheel rotates the solution is continually dispensed on the wheel from the hopper 44. The heat from the heating chamber 8 and the hot air from the air chamber 50 assist in evaporating the solvents from the solution and removing the solvents from the vicinity of the wheel. When enough of the solvent has been removed, the web becomes self supporting whereupon it is removed from the wheel as shown.

FIG. 4 also shows the water level in the heating chamber 8; the number 60 indicates the water level at 50% and the number 62 indicates the level at 99%. The cooling chamber level is shown in FIG. 4 with the number 64 indicating the level at approximately 50% and the number 66 indicating the level at approximately 98%.

A partially filled cooling chamber 22 has been found to transfer heat much more effectively than other systems. The cooling chambers are filled to approximately 50% to 98% of capacity although slightly more or less could be used. As previously discussed, the transfer of heat across a completely filled chamber is inefficient as compared to the transfer of heat across a partially filled chamber. This invention utilizes that concept to more effectively remove heat from a casting wheel in addition to providing heat to the casting surface.

The invention has been described in considerable detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

1. A wheel for casting, transporting, and drying a web comprising:

an outer cylindrical sheel having a smooth surface for receiving a web thereon;

an inner shell spaced from and concentric with said outer shell;

plate means connecting said shells to define a sealed chamber therebetween;

heat-conductive fluid partially filling said chamber;

heating means mounted contiguous to the inner shell for heating the inner shell;

means for rotating said wheel and chamber about a substantially horizontal axis to move the chamber relative to the heat-conductive fluid and to mix that portion of fluid immediately adjacent to the inner shell of the chamber with the remainder of the fluid in said chamber, whereby heat is transferred from the inner shell to the outer shell of the chamber through the mixed heat-conductive fluid.

2. The invention according to claim 1 wherein said heating means comprises a serpentine coil extending transversely the surface of and along the inner circumference of said inner shell.

3. The invention according to claim 1 wherein said chamber is between 50% to filled with heat-conductive fluid.

4. A cylindrical shell having a smooth surface for forming a web cast thereon comprising:

means defining sealed cooling chambers extending along the inner circumference of said shell adjacent the edge portion thereof;

heat conductive liquid partially filling said cooling chambers;

means for conducting cooling fluid through the heatconductive liquid in the cooling chamber to remove the heat therefrom;

means for rotating said shell about a horizontal axis to mix that portion of liquid immediately adjacent the outer shell with the remainder of liquid in said cooling chambers to transfer heat from the outer shell to said conducting means.

5. A wheel for casting, transporting, and drying a web comprising:

an outer cylindrical shell having a smooth surface for receiving a web; an inner shell spaced concentrically from said outer shell and positioned such that the ends of the outer shell extend beyond the ends of the inner shell;

plate means extending radially between said inner and outer shells to define a sealed heating chamber therebetween; means defining sealed cooling chambers extending along the inner circumferences of said outer shell at those end portions that extend beyond said inner shell;

heat-conductive liquid partially filling said heating chamber and said cooling chambers;

heating means mounted contiguous to the inner shell for heating the inner shell to appl heat to the heatconductive liquid in the heating chamber;

means for conducting cooling fluid through the heatconductive liquid in the cooling chambers to remove the heat therefrom;

means for rotating the heating and cooling chambers around a horizontal axis such that the portion of fluid in the heating chamber adjacent the inner shell mixes with the remainder of the fluid in the heating chamber, thereby transferring heat from the inner shell to the outer shell and such that the portions of fluid in the cooling chambers immediately adjacent the outer shell mix with the remainder of fluid in the cooling chambers, thereby transferring heat from the outer shell to the conducting means to remove heat from the edge portion of the outer shell whereby an even temperature is maintained across the surface of said outer shell.

6. The invention according to claim 5 wherein said cooling chambers are between 50% to 98% filled with heat-conductive fluid.

7. The invention according to claim 5 further comprising:

means for supplying air to a portion of the surface of said wheel;

8 means for removing the air from the vicinity of said wheel.

References Cited UNITED STATES PATENTS 1,008,607 11/1911 Mellinger et al 18-1-5 2,806,250 9/1957 Wallis 18-15 3,142,866 8/1964 Pabo l8-l5 H. A. KILBY, JR., Primary Examiner mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,534,438 Dated October 20, 1970 Inventor) Donald W. Bushnell, Waldemar Pabo It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

1. In column 6, line 8, "sheel" should be --shell-. 2. In column 6, line 30, "90%" should be "99%".

5.52am MD SEhLED JAN 5 I 71 Amt:

Edmrdu my. 3: =4; a.

Auesting Offiw' mumma: mm: 

